1. Field of the Invention
The present invention relates to a printing apparatus implemented in the form of a printer, a typewriter, word processor or like equipment using an ink ribbon for printing purposes.
2. Description of Related Art
Printing apparatuses that use an ink ribbon cassette are well known. In the typical printing apparatus, the ink ribbon cassette is removably mounted on a carriage. When a user operates a print start button or like switch, not shown, the unused ink ribbon wound inside the ribbon cassette starts to be fed toward the printing area of the apparatus in synchronism with its continuous printing operation. In this type of machine, when the unused ink ribbon inside the ink ribbon cassette has reached its end, no more printing is available. There have been proposed printing apparatuses having mechanisms for detecting the end of the ink ribbon. When the detecting mechanism detects the ink ribbon end during operation, the printing apparatus stops further printing action and issues a message prompting the user to change the ink ribbon cassette. One such detecting mechanism is disclosed in Japanese Patent Laid-Open No. Sho 61-195882. This mechanism, using a reflection type photosensor and operating in a printing apparatus, works as follows. A silver-colored reflective tape is attached to the end of the ink ribbon. When the reflection type photosensor detects a difference between the reflection from the tape surface and the reflection from the reflective tape, the photosensor interprets the difference as an indication of the end of the ink ribbon. One disadvantage of this mechanism is its poor reliability. That is, the photosensor can malfunction if the ink ribbon is not the usual black ribbon but a color ribbon that reflects incident light better. Because some color ribbons reflect light better than the black ribbon, the reflected light from the tape can be erroneously interpreted by the photosensor as the end of the ribbon. This stops the printing operation even though a large usable portion of ink ribbon still remains inside the cartridge. Another disadvantage is that a reflective tape is attached to the end of every ink ribbon, to thus increase a cost of the ink ribbon.
Other printing apparatuses are proposed to be equipped with a microswitch instead of the photosensor to detect the end of the ink ribbon. Such printing apparatuses are disclosed in Japanese Patent Laid-Open Nos. Sho 61-95975 and Sho 57-199680. On these machines, when the ink ribbon has come to its end, the tension of the ribbon deforms an actuator inside the ink ribbon cassette. In turn, the deformed actuator turns on the microswitch. A controller connected to the microswitch then detects the end of the ink ribbon.
The microswitch-equipped ink ribbon end detecting mechanism detects reliably the end of the ink ribbon regardless of the ink ribbon color. However, this mechanism is provided only to make sure that the ink ribbon has indeed come to its end; it fails to detect other ribbon-related irregularities such as incorrect setting of the ribbon cassette.